Spontaneous and piezoelectric polarization effects in wurtzite ZnO/MgZnO quantum well lasers

Spontaneous and piezoelectric polarization effects on electronic and optical properties of ZnO/MgZnO quantum well (QW) structures are investigated by using the non-Markovian gain model with many-body effects. The spontaneous polarization constant for MgO determined from a comparison with the experiment is about -0.070 C/m², which is larger than the value (-0.050 C/m²) for ZnO. The negligible internal field effect observed in the case of ZnO/MgZnO QW structures with relatively low Mg composition (x≪0.2) and thin well width (L_w≪46 Å) can be explained by the cancelation of the sum of piezoelectric and spontaneous polarizations between the well and the barrier. The ZnO/MgZnO QW laser has much larger optical gain than the GaN/AlGaN QW laser. This is attributed to the fact that the ZnO/MgZnO QW structure has a larger optical matrix element due to the relatively small internal field, compared to the GaN/AlGaN QW structure.